1. Field of the Invention
The present invention relates to antenna systems for a dual-transmission single broadcasting service and more particularly to dual-antenna systems for vehicles for receiving both satellite and terrestrial transmission signals.
2. Description of the Related Art
A variety of dual-transmitter broadcasting formats are under development and service. Two of such formats those identified by the trademark SIRIUS RADIO and the trademark XM RADIO. Both satellite and terrestrial transmitters transmit the signal simultaneously. The satellite can cover the vast area, however, it can""t cover all areas the area out of satellite coverage such as building blocking place. The terrestrial transmissions in urban areas will complement satellite transmission. For such applications antennas are required to receive the dual-transmission signals.
Generally, the antennas adapted for use with a vehicle is capable of receiving only the linearly polarized signals from terrestrial transmitters. Consequently, vehicle antenna must be complicated and augmented for the reception of signals from both the satellite transmitter with the circular polarization and from terrestrial transmitter with linear (usually vertical) polarization.
U.S. Pat. No. 6,329,954 issued to Andreas on Dec. 11, 2001, discloses a dual-antenna system, appropriate for automotive applications, which is capable of receiving both satellite transmission signals and terrestrial transmission signals. The antenna system is adapted to be mounted on the roof of the vehicle. The antenna system includes a radome, a satellite cross dipole antenna, a terrestrial monopole antenna elements, and a printed circuit board with feeder systems and low noise amplifiers (LNA) circuitry. The terrestrial antenna radiation pattern needs to have maximum gain for a low elevation angle, from 5 degrees up to 20 degrees and using vertical polarization. In the case of satellite antenna, the elevation angle must be typically in the order of 60xc2x125 degree, and circular polarization (left-hand or right-hand) must be used. In either case, the radiation pattern must be omni-directional in azimuth.
However, due to a poor satellite link budget, the satellite antenna needs to be able to work on signal level less than xe2x88x92120 dBW. The antenna passive gain at 60 degree elevation angle must be more than +3 dBic with CP axial ratio  less than 0.5 dB and LNA noise figure specified at level 0.6xe2x88x920.9 dB. Therefore, feeder insertion loss between antenna active (radiating) elements and LNA input extremely important for the satellite antenna system performance.
U.S. Pat. No. 5,317,327 issued to Philippe on May 31, 1994, discloses a skirt-helix assembly, in which the terrestrial signals received by the skirt antenna and a satellite signal received by the helix antenna, two signals are combined in a coupler with adequate isolation between its two input channels. To increase the level of the satellite signal and to compensate for the insertion loss, an amplifier must be provided in the helical antenna circuit on the input side of the coupler. U.S. Pat. No. 6,150,984 issued to Akihiro, et al. on Nov. 21, 2000, discloses a composite shared antenna for both satellite communications and terrestrial communications and proposes a patch-shaped radiating element with connection to a linear antenna or a single-line helical antenna.
However, the antenna systems of prior art are non-planar system so not suitable for a low cost surface mount mass production assembly technology. Another problem of prior art is that most antenna structures are so bulky and large profile that the size of the antenna may become a critical point for the rooftop mount vehicle application.
As another significant disadvantage for prior art is the frequency wideband response for the cross dipole, helical, and monopole radiating antenna elements causing an interference problems with wireless networks and different spectrum radio communication signals.
The object of the present invention is to provide a dual-antenna system overcoming the problems mentioned above, which can be implemented on a Satellite Digital Audio Radio Service (SDARS) for the vehicle and other mobile and portable applications.
It is another object of the present invention to provide a low profile and compact dual-antenna system suitable for the surface mount mass production assembly technology with the improved out-of-band signal rejection, cross polarization purity, and the maximally possible sensitivity.
The antenna system is capable of receiving both satellite transmission signals and terrestrial transmission signals. The antenna system includes a first antenna for receiving circular polarized satellite transmissions and a second antenna for receiving linear polarized terrestrial transmissions. The terrestrial antenna is an array of radiating elements arranged in a symmetrical configuration with respect to the satellite antenna. Satellite antenna is also array antenna. It is circularly polarized 2xc3x972 array of linearly polarized single feed patch elements with angular and phase arrangement, which generates a circularly polarized beam
The present invention provides the antenna structure comprising a mounting substrate, having opposing top and bottom faces. On the top face are mounted a first backgrounded dielectric substrate having a circularly polarized 2xc3x972 patch array as a satellite antenna radiating element. A second dielectric superstrate covers the first dielectric substrate with satellite antenna elements. The superstrate has a high dielectric constant.
The terrestrial antenna in array elements are mounted on a top face of mounting substrate and arranged in a symmetrical configuration around the first dielectric substrate having a satellite antenna radiating elements. The terrestrial antenna includes four linearly polarized radiating elements arranged in an array with a conical beam radiation pattern. Each antenna element has a quarter lambda grounded microstrip resonatorxe2x80x94the surface mounted planar inverted F-antenna.
The satellite and terrestrial antennas radiating element arrays are concentricxe2x80x94the physical center of the each antenna array being same.
Electronic module with circuitry for signal amplification and filtering is mounted on a mounting substrate bottom face. A radome covered a mounting substrate with surface-mount antennas and electronic module. A radome has a bottom housing section and a top housing section, which are integrally joined together to hold weatherproof an antenna assembly therein.
A mounting substrate is a multi-layer printed circuit board with a planar feed networks having a first feed element""s layer for the satellite antenna and a second feed element""s layer for the terrestrial antenna.
A satellite antenna radiating element is an 2xc3x972 patch array antenna having four microstrip patch antenna elements that a linearly polarized. Patch elements arranged by two crossed couples as balanced doublets. The patch feed-point phase arrangement has sequence of 0, 180, 90, 270 degrees.
The patch feed-points have a balanced active (with gain) feeding to satellite antenna outputs (to receiver) with a good rejection to common mode signal received by patches. A common mode signal means non-differential (non- 0/180 or 90/270 degree) patch excitation. Therefore, significantly improved antenna performance will be for cross-polarization rejections, especially for the low angle elevation signals.
One of the novel features of the present invention is the elimination of insertion loss brought by a conventional feeder system (passive feed network for phase arrangement) placed between the LNA input and radiating patch feed-points. Significantly improved the satellite signal/noise ratio by virtue of in-antenna signal amplification on the radiating (receiving) patch array side, so-called xe2x80x9cactivexe2x80x9d antenna.
The patch antenna elements are printed on a backgrounded dielectric substrate located on the top face of the mounting substrate. A superstrate covers the satellite antenna elements. The superstrate has a high dielectric constant, which reduces the physical size of a wavelength of electromagnetic wave at the design frequency so that the size of the antenna elements can be reduced.
The superstrate also suppresses the cross-polarization generated by higher-order modes within the patches and this improves axial ratio at low angles for signal from low elevation satellite.
Another advantage, over the conventional ceramic patch antenna is much less patch resonance frequency sensitivity to the ceramic material dielectric constant tolerance, hence lowering production cost.
Another advantage with the present invention is that the patch antenna has a narrow bandwidth, compared to prior art antennas, more suitable for SDARS applications, for prevent out of band radio interference.
The proposed dual-antenna system structure is suitable for the conventional surface mount mass-production assembly technology.
Still another advantage is that the present invention has a low built-in antenna height compared to prior art antennas. The proposed antenna improves the cosmetic appearance of the vehicle with SDARS.